1. Field of the Invention
The present invention relates to circuit modules mounted in communication equipment, etc., and more particularly relates to a circuit module such as a surface mountable DCxe2x80x94DC converter. The present invention also relates to a method for mounting the circuit module on a mother circuit board incorporated in communication equipment, etc.
2. Description of the Related Art
Recently, circuit boards incorporated in communication devices have been loaded with circuit modules along with various electronic components. From the viewpoint of working efficiency, the process of mounting the electronic components, etc., is preferably automated. To this end, each of the electronic components is formed to have a shape suitable for being chucked and carried by a chucking device. As described in Japanese Unexamined Patent Application Publication No. 8-107024, for example, a component such as a transformer formed by winding a conductive wire is covered with a special casing so as to facilitate the chucking process performed by the chucking device.
This will be more specifically described below with reference to FIG. 13. A bobbin 1 around which a coil is formed is combined with end portion supporting plates 2 and 2 which are provided under the bobbin 1 at both ends in the axial direction. Lead terminals 3 and 3 horizontally lead out from the end portion supporting plates 2 and 2. A conductive wire is wound around the bobbin 1 to form the transformer coil. A pair of E cores 4 and 4 are fixed with the bobbin 1, projections at the midsections of the E cores 4 and 4 being fit into the central opening of the bobbin 1 from both sides in the horizontal direction. The bobbin 1 and the E cores 4 and 4 are covered with a casing 5 which has an upper plate 6 with a flat surface. The casing 5 includes core clamping portions 7 and 7 for interlocking the pair of E cores 4 and 4 with each other. The clamping portions 7 and 7 are extended vertically downward from the two opposing sides of the upper plate 6 and are bent. In addition, the casing 5 also includes bobbin crimping portions 8 which are extended downward from the other two opposing sides of the upper plate 6 and are bent. The bobbin crimping portions 8 prevents the rattling of the bobbin 1 and the E cores 4 and 4. This unit is mounted on a circuit board by chucking the upper surface of the casing 5 at the midsection thereof with the chucking device.
With regard to a circuit module in which electronic components are mounted on a small circuit board at high density, however, the circuit module cannot be chucked and lifted by the chucking device since the electronic components form concavities and convexities on the circuit board. A communication device, for example, includes a power supply for providing electric power, and a DCxe2x80x94DC converter is separately mounted on a mother circuit board which is incorporated in the communication device. The DCxe2x80x94DC converter contains transformers, rectifiers, switching transistors, ICs, capacitors, etc., on a multi-layer circuit board provided with electric wires not only on the surface but also between the layers. Such a circuit module weighs 5 to 10 g, which is much heavier than other electronic components. Accordingly, even when a transformer having the above-described construction is used, the circuit module cannot be lifted and carried since the upper surfaces of the electronic components are not large enough to allow the required chucking force.
In addition, since circuit modules such as DCxe2x80x94DC converters are mounted on mother circuit boards incorporated in communication devices, the circuit modules are required to be as light and thin as possible. The electronic components mounted on the DCxe2x80x94DC converter differ in height, and the tallest component of all is generally the transformer. Thus, to make the DCxe2x80x94DC converter thinner, the inventors have used, instead of the transformer having the above-described construction, a transformer formed by the following process. The multi-layer circuit board is used as the circuit board of the DCxe2x80x94DC converter, and ring-type or helical-type coil patterns are formed by utilizing the surface and the region between layers of the multi-layer circuit. The coil patterns are connected by via holes so as to form two coils with the required numbers of windings. Through holes are formed at the center and in the surrounding region of the coils, and leg portions of cores are inserted into the through holes. The cores are fixed to the circuit board with a metal fitting, so as to from the transformer.
Even with the above-described constructions, the cores fixed to the multi-layer circuit make the transformer the tallest component compared to other electronic components. For making such a circuit module chuckable by the chucking device, the inventors have experimentally manufactured circuit modules having a chucking surface. The chucking surface was formed by disposing a chucking plate over the core, the tallest component, and the next tallest of the electronic components, by applying several tens of milligrams of an adhesive with high viscosity.
The electronic components mounted on the multi-layer circuit board, however, differ in height, and thus it is difficult to maintain the chucking plate parallel to the surface of the multi-layer circuit board. Accordingly, there is a risk that the chucking plate will tilt relative to the multi-layer circuit board. When the chucking plate tilts by 2xc2x0 relative to the multi-layer circuit board, for example, the chucking device cannot chuck and carry the circuit board.
In addition, the cores fixed by the metal fitting rattle in the through holes formed in the multi-layer circuit board. Accordingly, it is difficult to maintain the chucking plate parallel to the multi-layer circuit board when the chucking plate is fixed over the cores and another electronic component. Thus, the workability is degraded.
Furthermore, the viscosity of the adhesive to fix the chucking plate on the electronic components is high, so that it is difficult to apply small amounts of adhesive such as several tens of milligrams. Accordingly, there is a risk that the adhesive will soften during the process of heat curing so that the chucking plate moves by itself, and there is also a risk in that the adhesion force may not be sufficient so that the chucking plate moves while the circuit module is carried into a curing oven. Thus, there is a risk that the chucking plate cannot be placed at a predetermined position.
Furthermore, in addition to the process of reflowing for fixing the electronic components on the circuit board as surface mounted devices, the process of applying the adhesive manually and the process of heat curing are required. Thus, the number of processes is increased and the automated assembly is interrupted, providing drawbacks in that the accuracy of the processing and the working efficiency are degraded.
Accordingly, an object of the present invention is to provide a circuit module which realizes an automated mounting process.
Another object of the present invention is to provide a method for mounting a circuit module on a mother circuit board.
The circuit module of the present invention comprises a covering member which has a plate portion and one or more supporting portions and a circuit board on which electronic components are mounted. The supporting portions fix the plate portion to be parallel to the surface of the circuit board. According to the structure, the covering member is directly attached to the circuit board, and the plate portion of the covering member is supported in parallel to the circuit board. Accordingly, the tilt of the plate portion is small, and sufficient area for chucking is provided when the chucking device chucks and lifts the circuit module. Thus, chucking and carrying of the circuit module are more reliably performed by the chucking device.
In addition, the covering member is fixed to the circuit board using the through holes formed in the circuit board and the attaching portions of the supporting portions provided to the covering member. Thus, the process of attaching the covering member is extremely simplified, providing improved workability. The core unit is supported by the supporting portions, and is pressed against the surface of the multi-layer circuit board by the plate portion of the covering member. Accordingly, the cores are retained at the predetermined position, so that the cores do not rattle or move. When the pressing portion for pressing one of the cores against the inner walls of the through holes is additionally applied, the core may be retained in any direction in three dimensions. This stabilizes the magnetic condition of the transformer.
The covering member is preferably attached directly to the multi-layer circuit board. Accordingly, the plate portion may be laid on one of the electronic components mounted on the multi-layer circuit board so as to ensure that the plate portion is parallel to the multi-layer circuit board, and sufficient area for chucking is provided. Thus, the covering member does not tilt relative to the chucking device, and the circuit module, which is much heavier than independent electronic components, may be reliably chucked and carried by the chucking device. In addition, the plate portion of the covering member may be disposed at the center of the multi-layer circuit board, so that the circuit module may be lifted by the chucking device at the center of gravity and be carried in a balanced manner.
In addition, the step portion and the hook portions of the attaching portions provided to the covering member fix the covering member to the multi-layer circuit board. Accordingly, the process of attaching the covering member is extremely simplified, providing improved workability. In addition, the coils of the transformer are formed at the same time the electric wires are formed in the multi-layer circuit board. Thus, the transformer is formed simply by attaching the core to the multi-layer circuit board. Furthermore, the core unit is fixed using the covering member so that the cores are easily prevented from rattling or moving relative to the multi-layer circuit board. Accordingly, the number of processes for manufacturing the circuit module is reduced, and an automated manufacturing process may be realized, providing improved working efficiency.
In addition, the plate portion of the covering member may be provided with the protrusion at the bottom surface with which another electronic component supports the plate portion. With such a construction, the plate portion may be maintained to be parallel even when the plate portion is thin or long. Accordingly, vibration or impact force applied to the plate portion may be spread out, and an excessive stress applied to the supporting portion may be relaxed.
The circuit module formed by mounting electronic components on the daughter circuit board is much heavier compared to other independent electronic components. With the method for mounting the circuit module in accordance with the third aspect of the present invention, however, such a circuit module may be mounted on the mother circuit board by using the chucking device in the same way as for the other electronic components. This is achieved by providing the chucking plate on the circuit board. Accordingly, the manufacturing of the circuit board contained in communication equipment, etc., may be automated, significantly improving working efficiency.